The invention relates to the control of composite filter rods prior to sectioning of them into, for example, cigarette filter tips.
The automatic, continuous manufacture of composite filters, i.e., filters comprising two or more distinct elements, generally takes place by placing filter elements end-to-end on a moving band of paper passing through a wrapping and sealing or glueing device to form a rod which is then cut into sections each forming a filter unit or tip. The filter elements may for example be plugs of different nature, or hollow plastics material bodies which may or may not contain granules and are placed between two plugs of paper or another material. Such filters and their manufacture are described for example in U.S. Pat. Nos. 3,551,256 and 3,610,112. However, it can happen that a filter element is missed out and produces a gap in the rod, which cannot be visually observed through the opaque envelope. The rods may also have other faults such as spaces left between adjacent plugs which should be contiguous, or cavities which are insufficiently filled with granules of carbon, for example.
An aim of the invention is to provide a device for detecting such faults in filter rods after the formation thereof and as they are fed towards a sectioning device, to enable elimination of faulty sections immediately after sectioning without having to interrupt or slow feed of the rod.
A gap of 0.5 mm in a filter rod is considered as an inacceptable fault, and it is consequently an aim of the invention to provide a control device that may be constructed and arranged to operate to such a precision, and to react rapidly.
In existing machines, the detection of faults in the filter rod must in general be carried out in a very restricted space, and a further aim of the invention is to enable this condition to be satisfied.